This invention relates generally to bulk containers and more particularly to bulk bags, and liners for bulk bags or other bulk containers, which are collapsible and formed of a flexible material.
Many granular and liquid products have been shipped and stored in large bulk bags which may contain as much as a ton or more of material. Some of these bulk bags are flexible, contain a liner, and when empty can be folded to a generally flat condition. One such flexible bag and liner is disclosed and claimed in U.S. Pat. No. 5,104,236. These flexible bags and liners for bulk containers, have been formed from a single tubular blank of material to form generally rectangular ends interconnected by generally rectangular side walls. When filled, these bags can be stacked one on top of another. For some applications, the bags may be made of a woven fabric and for other applications, a plastic sheet material. For some applications, particularly for storing liquids, a bag or liner of a water or liquid impervious sheet material is received in and reinforced and protected by bag of a woven fabric. Usually these bags have a spout in one or both ends for filling and emptying the bags.
To provide a bag having walls formed from more than one layer of material, one bag has been stuffed into another bag of generally the same configuration, such as a liner being stuffed into a bulk bag. Unfortunately, it is difficult to accurately align the inner bag or liner with the outer bag and the inner liner may become bunched up or otherwise folded or creased within the outer bag. Upon filling, localized stresses occur within the inner bag or liner decreasing its effectiveness and potentially leading to a rupture of at least the inner bag or liner.
A bulk bag or a liner for a bulk container is formed from a plurality of tubular blanks of flexible material so that each wall of the bag or liner is formed from at least two layers of material. Desirably, many woven or plastic sheet materials suitable to make such bags or liners are available in elongate and circumferentially continuous tubular webs such that a plurality of liners or bags may be formed connected in end to end relation on an elongate web. In one form, a pair of gusseted tubular blanks are disposed between and sealed to a pair of overlying flat tubular blanks to define the liner or bag having a plurality of walls each formed from two layers of material. In an other form, a pair of tubular blanks are folded so that each tubular blank defines one flat panel and one gusseted panel and the tubular blanks are heat sealed together along a pair of side edges of the liner or bag to also define a liner or bag wherein each wall is formed from two layers of material. In still another form, a gusseted tubular blank may be disposed inside of or outside of either of the previous forms of the invention to provide a liner or bag having each wall formed of three plies or layers of material. In any form, a multiple layer bag or liner is provided with each wall formed from multiple layers of material and with each layer of each wall properly positioned and without having to stuff one bag or liner into another bag.
Objects, features and advantages of this invention include providing a bulk bag or liner which has each wall formed from multiple layers of material, accurately aligns and maintains in position, the various layers of material of each wall, reduces the likelihood of leakage of the contents of the bags, reduces the likelihood of rupture of any wall or seam, permits a plurality of bags to be readily formed from an elongate web of material, facilitates the manufacture of bags having walls formed from two or more layers of material, facilitates forming a plurality of bags from elongate tubular webs of material, is of relatively simple design and economical manufacture and assembly, and can be produced by a method which is substantially automated, efficient and relatively simple to perform.